One Rep Max (1RM) Calculator
Estimate the most you could lift for a single rep, safely, from a lighter set of multiple reps. Includes a percentage chart for your training.
Your result appears here.
By Shah Rukh, software developer · Last updated:
The formulas
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Example: 100 kg for 5 reps gives about 116.7 kg (Epley) and 112.5 kg (Brzycki), so roughly 115 kg.
Using percentages
- 85–95%: heavy sets of 1–5 reps for strength.
- 70–85%: 6–12 reps for muscle growth.
- Below 70%: technique, warm-ups and endurance.
Estimates are most accurate with sets of 10 reps or fewer. Always lift with good form, and use a spotter for heavy attempts.
Frequently asked questions
Is it safe to test a true 1RM?
It carries more risk. An estimate from a 3–5 rep set is safer for most people.
Why do the formulas give different numbers?
They were built from different data. Averaging them gives a sensible estimate.
Does it work in pounds?
Yes. The result is in the same unit you enter.
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